And if you haven't disabled your automated updates in Ubuntu Linux, then as soon as they release it you should have it automatically install it. But since I have manually disabled the update manager because it uses too much of your bandwidth which can result in a cluttered YouTube videos :D (kidding, again, but I do have it disabled for other reasons)...
I've also been a bit busy yesterday and until I manually check this morning I didn't know it was available to Natty users. Anyhow, to install it (in my humble opinion, I think unlike with other releases, FF6 is well worth the update because as promised by Mozilla, it loads itself pretty faster than the previous versions) , perhaps you should re-enable the update manager t OR
just fireup your Terminal window and enter the below command to install the sucker!.
sudo apt-get install firefoxIf you'd prefer a more cleaner installation, then first remove your current Firefox browser completely (make sure to take back-ups of your Bookmarks and other naughty stuff), then use the below command first.
sudo apt-get purge firefox
That should do it.